1. Field of the Invention
The invention relates to the field of telephone station sets, particularly those employing hook switches.
2. Prior Art
Typically, in telephony, a handset or the like, rests on a hook switch. Lifting the handset from the hook switch couples the set to a pair of leads (TIP and RING); this off-hook condition is detected by sensing current flow which increases. Likewise, restoring the handset to the cradle depresses the hook switch, permitting an on-hook condition to be sensed.
In some telephony systems, the duration of the on-hook or off-hook condition is used as a means for transmitting additional information. Generally, the hook switch is manually (and rapidly) depressed, providing "flashing". This hook switch flashing in some systems accesses features such as call transfer, establishment of conference calls, parking, hold and others. By way of example, a private branch exchange (PBX) may have a flash window between 300-900 msec. If the current is interrupted for greater than 900 msec. (typically 1.5 seconds), a hang-up is assumed.
A problem with hook switch flashing is that it relies upon the caller's sense of timing and is considered by some to be inconvenient. A caller, after completing one call, may manually depress the hook switch, but only momentarily before beginning another call. This momentary depression, if interpreted as a flash, can result in a phantom ring-back. In other instances, a caller may depress the hook switch for too long a period, and then an intended flash may be interpreted as a hang-up.
As will be seen, the present invention provides a telephone station set with a separate flash button. Depression of the flash button assures flash signalling; depression of the hook switch assures the signalling of a hang-up.